JPH02241082A - Post desmear processing of printed board - Google Patents

Abstract

PURPOSE:To enable any residual smear on an inner layer conductor to be removed while improving the connection between respective layers by later through hole plating process as well as enhancing the reliability of a printed board by alkali electrolytic processing after desmear processing. CONSTITUTION:After desmear processing, alkali electrolytic cleaning process is performed. The applicable electrolyte 4 in this process is composed of e.g. sodium hydroxide 30g/l, sodium carbonate 10g/l, sodium gluconic acid 5g/l, EDTA 0.5g/l while the copper foil layer in a printed board 1 works as an anode and a carbon 3 works as a cathode. Besides, voltage of 5V, temperature at around 30+ or -5 deg.C and processing time of around 5 minutes are specified. Later, the printed board 1 is washed and then neutralized using sulfuric acid in 5% concentration for around 2 minutes. Through these alkali electrolytic processing, oxygen is produced not only from the surface of processed holes 11 as through holes but also from the surface of inner layer conductor so that any smear crept in the surface of the inner layer conductor may be removed.

Description

[Detailed Description of the Invention] [Summary] To provide a desmear post-processing method that can more completely remove smear, regarding a desmear post-processing method in a processed hole for a through hole, and to further improve the reliability of a printed circuit board. For this purpose, the holes in the printed circuit board are made by desmearing the inner wall of the through-hole after processing, and then electrolytically treating it in an alkaline solution.

[Industrial application field]

The present invention relates to a method for manufacturing a printed circuit board, and more particularly to a method for post-desmear processing in a processed hole for a through hole.

[Prior art]

In a printed circuit board, first, inner layer conductors are formed, and then prepreg is sandwiched between each inner layer conductor and laminated by heat processing, and then processed holes that become through holes are made. Thereafter, a surface pattern and through-hole plating are formed through a process such as electroless plating or electrolytic plating.

Since the drilling process is performed using a drill, the resin melts due to the cutting heat of the drill and adheres to the surface and inner conductor surfaces, resulting in so-called smear S (see FIG. 4). When this smear occurs, connectivity between the through-hole plating layer and the conductors in each layer is lost. Therefore, a desmear process is performed to remove the smear.

FIG. 3 is a process diagram showing the procedure of desmear treatment using permanganic acid, and FIG. 4 is a sectional view of a printed circuit board showing an example of the smear.

First, the printed circuit board 1 after lamination is processed to form holes 11 for through holes (step 5ll), and then resin swelling treatment is performed with an ether solvent (step S12: soften the smear. The smear is then soaked in a potassium permanganate or sodium permanganate solution to remove the smear (step 5).
13).

At this time, the permanganic acid solution partially penetrates into the material that makes up the printed circuit board, and if left as it is, it will have a negative effect on the insulation, so next it is neutralized with a sulfuric acid neutralizer (step 51).
After 4), electroless plating and electrolytic plating processing (step 515) are performed, and thereafter, a surface pattern and through holes are formed through pattern plating (electrolytic plating) and the like.

In addition to the method using permanganic acid as described above, desmear treatment includes a chromic acid method, a sulfuric acid method, and a method of plasma treatment in a gas mainly composed of chlorofluorocarbons, which are used selectively depending on the substrate material, etc. There is.

[Problem to be solved by the invention]

The desmear process described above is performed by etching the resin on the surface of the processed hole for the through hole, and is quite effective in removing smear adhering to the surface. At present, the smear S that has adhered to the surface cannot be completely removed. Therefore, plating chipping occurs in this portion, resulting in poor inner layer connections and a problem in that the printed circuit board lacks reliability.

This invention has been proposed in view of the above-mentioned conventional circumstances, and aims to provide a desmear post-processing method that can more completely remove smear, and further improve the reliability of printed circuit boards. It is something.

[Means to solve the problem]

In order to achieve the above object, for example, as shown in FIG. 1, the holes in the printed circuit board 1 are made by desmearing the inner wall of the through-hole hole 11 after processing, and then in an alkaline solution 4. It is designed to undergo electrolytic treatment.

[For production]

Due to the electrolytic treatment in the alkaline electrolyte, oxygen gas generated from the printed circuit board side of the positive electrode cleans not only the inner circumferential wall surface of the processed hole but also the upper surface of the inner layer conductor 11.

〔Example〕

FIG. 2 is a process block diagram showing the desmear processing procedure of the present invention. After drilling a hole for a through hole, a resin swelling treatment is performed using an ether solvent (step Sl), and then a permanganate treatment (
Step 32) and then neutralize with a sulfuric acid neutralizer (
Step S3).

The desmear process described above is completely the same as the conventional process.

After this, alkaline electrolytic cleaning according to the present invention is performed (step 4). The electrolytic solution 4 used at this time is, for example, 30 g/l of sodium hydroxide, Log/l of sodium carbonate.
, sodium gluconate, 5 g/It, and EDTA (ethylenediaminetetraacetate), 0.5 g/41, as shown in FIG. 1, the copper foil layer of the printed circuit board 1 serves as an anode, and the carbon 3 serves as a cathode. Also, the voltage is 5V and the temperature is 30±5℃
The processing time is about 5 minutes. After that, it is washed with water and neutralized with 5% sulfuric acid for about 2 minutes.

Incidentally, it goes without saying that a hot water washing or water washing step is also included between each of the above steps 81 to 35.

By the alkaline electrolytic treatment as described above, oxygen is generated not only from the surface of the processed hole 11 for the through hole but also from the surface of the inner layer conductor 12, and the smear that has penetrated into the surface of the inner layer conductor 12 is also removed.

[Effects of the Invention] As explained above, in this invention, smear residue on the inner layer conductor can be removed by alkaline electrolytic treatment, and the connectivity between each layer can be improved by the subsequent through-hole plating treatment. The reliability of printed circuit boards can be improved.

[Brief explanation of drawings]

Figure 1 is a diagram showing the principle of this invention, Figure 2 is a process diagram showing the procedure of this invention, Figure 3 is a process diagram showing the procedure of conventional desmear processing, and Figure 4 is an enlarged view of the machined hole. . In the figure, 1... printed circuit board, 11... processed hole, 4... alkaline solution. Desmith processing process diagram Figure 3 Enlarged view of the machined hole Figure 4

Claims (1)

[Claims] [1] After the printed circuit board (1) is drilled, the inner wall of the through hole (11) is subjected to desmear treatment, and then electrolytically treated in an alkaline solution (4). A desmear post-processing method for a printed circuit board, the method comprising: